There are various types of configurations in semiconductor fabrication apparatus. Generally, there have been used many semiconductor fabrication apparatus which are arranged such that a plurality of semiconductor substrates (wafers) are successively introduced from a cassette, and transferred between a plurality of processing devices by a plurality of transfer devices and processed concurrently thereby, and the substrates that have been processed are returned to the cassette. There have been known other semiconductor fabrication apparatus in which a plurality of cassettes can be mounted and replaced. Such semiconductor fabrication apparatus are continuously operable by replacing a cassette loaded with processed substrates with a cassette loaded with unprocessed substrates. Operation of these semiconductor fabrication apparatus, particularly the transfer devices, is controlled by a substrate transfer controlling apparatus.
A typical control process in a conventional substrate transfer controlling apparatus will briefly be described below.
The conventional substrate transfer controlling apparatus is continuously supplied with the statuses of transfer devices which are being controlled thereby. Based on the supplied statuses of the transfer devices, the substrate transfer controlling apparatus detects any transfer devices that are not in operation, i.e., any inoperative transfer devices. If the substrate transfer controlling apparatus detects any inoperative transfer devices, then it inspects, with respect to each of the inoperative transfer devices, whether there is a processed substrate in a processing device as a transfer source, whether there is an empty arm of the transfer device for receiving a substrate, and whether there is an empty processing device as a transfer destination. Then, the substrate transfer controlling apparatus determines all possible actions. Subsequently, with respect to each of the inoperative transfer devices where possible actions are present, the substrate transfer controlling apparatus determines an action to be performed next, and transmits a command for carrying out the action to the corresponding transfer device. In response to the received command, the inoperative transfer device starts the next action.
Specifically, if the substrate transfer controlling apparatus detects that the transfer device is inoperative at each point of time in the operation of the semiconductor fabrication apparatus, then the substrate transfer controlling apparatus determines whether or not a condition for carrying out a certain action to be done (operable condition) is satisfied. If there are any actions that satisfy the condition, then the substrate transfer controlling apparatus selects an action of highest priority and instructs the transfer device to perform the selected action.
The substrate transfer controlling apparatus repeats the above process to control the transfer of substrates in the semiconductor fabrication apparatus.
With the conventional substrate transfer controlling apparatus, only when the operable condition is satisfied, the inoperative transfer device moves from the present position to the position of a processing device where a substrate is to be delivered or received. Specifically, even when the transfer device is inoperative, since it cannot move before the operable condition is satisfied, the throughput of the semiconductor fabrication apparatus tends to decrease.
One solution is to modify the operable condition as much as possible to allow each transfer device to start moving early by predicting the processing end time in a processing device as a transfer source. Even if the operable condition is thus modified, since next actions are successively determined, when a plurality of substrates are successively processed, the time for the final substrate to be returned to the cassette after it has fully been processed is liable to be later than a logically possible value (earliest time).
Furthermore, from the viewpoint of process, semiconductor fabrication apparatus are generally desired to transfer a substrate which has been processed in a processing device promptly to a next processing device (the immediacy is required for the semiconductor fabrication apparatus). For example, when a substrate is plated, the plated substrate needs to be transferred immediately to a next processing device and post-processed for cleaning or the like because if the plated substrate were left as it is, it would be lowered in quality due to oxidization or the like. Specifically, a certain constraint relative to the time to operate a transfer device (in the above example, a condition that the waiting time of a processed substrate for a transfer device is zero) may be required.
However, in the conventional substrate transfer controlling apparatus, even if an operable condition with respect to an action of high priority is satisfied, the transfer device cannot immediately perform the action as long as the transfer device is in operation. Therefore, the conventional substrate transfer controlling apparatus cannot control the transfer of substrates in consideration of constraints relative to the time to operate a transfer device.
Consequently, it is necessary to conduct an advance simulation prior to operation of the semiconductor fabrication apparatus to confirm whether it is possible to perform a control process satisfying such a constraint. However, such a process is tedious and time-consuming. Alternatively, it is necessary to pose a limitation on an expected processing time for each type of processing device in order to satisfy a constraint relative to the time to operate a transfer device. Further, the demand for immediacy of operation of the transfer device cannot accordingly be met in some cases, thereby leading to a reduction in quality and yield. Alternatively, it is necessary to arrange a post-processing device which requires immediacy and a main processing device integrally with each other, thus resulting in a limitation on the apparatus arrangement.